Move some implementation specific content to "Implementations"
In doing so the wording was changed a little bit to again separate the fact that this is a document aimed at autoloader developers. The wording of these two clauses is informing users and autoloader developers equally.
Incorrect MAY removal.
Another accidental MUST swap.
Removed a lot of implementation detail from definitions
Also, the use of MUST and MAY again sets the scene that this document is only for what autoloaders should do. Autoloader developers will be following this document and know what they need to do, then MUST and MAY are left for where folders go, etc.
Merge pull request #209 from philsturgeon/psr4

Move some implementation specific content to "Implementations"